If you only had one stat available and you had to pick between two different running backs, you'd probably want to know how many yards each runner averaged per carry. A player's rushing yards is largely a function of his total carries, and that number is dependent on certain things beyond his control (the quality of the other RBs on the team, his coach's philosophy, and the scoreboard, for example). But yards per carry helps to level the playing field, and gets at exactly what we want to know.

Fortunately, we have lots of statistics available, so we don't need to use only yards per carry. So if you were building an NFL team you'd take Clinton Portis before Rock Cartwright, despite Cartwright's 3.0+ advantage in yards per carry last season.

This gets us to the problem of small sample sizes. When Shawn Bryson averaged 5.28 YPC on 50 carries in 2004, it was easy to dismiss his success. Many would claim that achieving a high yards per carry average on a small number of carries is easy. (Of course, when Willie Parker rushed for 5.81 YPC on 32 rushes, those people probably said he wasn't as good as his numbers either.)

You'll hear this argument a lot: it's easy to record a high YPC if you don't have many carries. Maybe they don't really mean easy, but at least easier. But just because people say it, doesn't make it true. It's undoubtedly true that it is easier to get all sorts of extreme YPC numbers with a small number of carries, and that includes really high (and really low) YPC averages. And RBs that are running well usually get more carries going forward than runners that don't do so well. So what do the numbers say?

The above table includes every RB's YPC average the past four years. If a RB had 87 carries, his totals were put in the "51-100" category. Some of these groups are really small -- in 2003, only three RBs had between 251-300 carries. The low carry group is by far the biggest, because about 80 RBs a year have 50 carries or less. Most of the other groups have between 10 and 25 players.

So what does this table tell us? The RBs with the fewest carries also have the lowest yards per carry average. Now be careful. This does not mean that it's harder for RBs with fewer carries to obtain a high YPC average. It just means that RBs with fewer carries also tend to average fewer yards per carry. They also may have a higher YPC average (more on that tomorrow).

As you could probably noticed, the NFL average jumps around a bit. The average YPC is relatively constant so it's probably not absolutely necessary to normalize each player's production by year, but it feels like the right thing to do. Here's the same data as above but instead of showing each group's average YPC, we're looking at each group's average YPC as a percentage of the league average yards per carry.

I think that table captures what we want a bit better. The runners with the fewest carries clearly average the fewest yards per carry. The RBs with the most carries also average the most yards per carry.

So what does this all mean? Well, it might not mean much. It's logical to assume that coaches give the most carries to the best RBs. Less talented RBs won't get as many carries, and we shouldn't expect them to do well just because they are only running two or three times a game. Something else might skew the data as well. If Joe Scrub is lucky enough to rush 120 times for 600 yards, his coach might give him an extra 40 carries. Even if he only averages three yards per carry on those additional touches, his YPC for the season will be 4.50, and he'll be in the 150+ bracket. So the RBs in the 150+ bracket will get a boost while the RBs in the 101-150 group will "lose" Joe Scrub's stats.

Now that we know it's not common for running backs to average a high number of yards per carry without a lot of carries, let's take a quick look at all RBs last year that averaged at least 4.5 yards per carry with fewer than 100 rushes.

Darren Sproles, Michael Turner, Justin Fargas, Maurice Hicks, Adrian Peterson, Ryan Moats, Leonard Weaver and Chris Perry are all young and talented runners that haven't earned much playing time yet in the NFL. All play behind some pretty good runners, but are only an injury away from seeing significant playing time.

Michael Pittman, Ron Dayne and Shawn Bryson are NFL vets that have seen some success after changing teams, but have had generally underwhelming NFL careers. Bryson and Pittman are both versatile RBs with career YPC averages of 4.0+ and soft hands, but neither looks to be a starter anytime soon.

There's only one RB on that list that is a projected starter in 2006, and it's Ron Dayne. Dayne's always been a controversial running back that seems to polarize NFL fans. Will he revive his career in Denver? Should we care more about the much larger sample size (most of his career in New York where he was a bust) or the significantly smaller but more relevant one (his success playing in Denver last year)? It's hard to say, and I don't think he was as impressive as his 2005 stats indicated, but the above data makes me think we probably shouldn't dismiss those numbers too quickly.

This entry was posted on Sunday, July 9th, 2006 at 11:06 pm and is filed under General, Statgeekery.
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Interesting post, Chase, but what I'd like to know is whether a high YPC average with few carries one year is a good predictor of future success. So, for instance, what happens to most of the running backs who had few carries, but a high YPC average, in the rest of their careers? Do they usually turn out to be great running backs, or do most of them fade into obscurity? What's the predictive ability of a few carries? That would be a neat follow up.

What I find interesting is that the 51-100 carries group performed better than any other group except the 251+ carries group, which is clearly "feature back" territory. The 51-100 group might be more interesting to study than the 1-50 group, which is probably littered with RBs with fewer than 10 carries and other "noisy" anomalies resulting from usage in less common game situations.

As far as Shawn Bryson is concerned, I can tell you from being an devoted (and unfortuante) Lions fan, that his yards per carry number is inflated by being the 3rd down back. In other words, he would receive a lot of carries on draws on 3rd and 9 or 3rd and 15 that would go for 6 and 7 yards each time. Even though he averaged 5+ yards per carry, he's running the ball in a situation where 5 yards would be considered a failed play.

On the other hand, a guy like Brandon Jacobs only received about 2.6 yards per carry, but his carries were limited to goal line situations.

So this is why I think you're right that the average yards per carry doesn't mean much for players with 0-50 carries. Those players are more likely to be situational backs whose yards per carry are influenced more by situation than actual talent. The average may simply demonstrate that more situational backs are short yardage backs rather than 3rd down backs. Perhaps this could be the key to the strange productivity that Jim A mentioned? Perhaps backs that touch the ball 51-100 times are more likely to be third down backs than short yardage backs?

Hey Nate. Here's the breakdown for Bryson and Jacobs. Bryson obviously benefitted significantly from the 77 yard run he had against the Ravens, and you accurately noted that Jacobs was used almost exclusively in short yardage situations.

Like most averages, YPC is a flawed statistic precisely because it can be greatly affected by a few long runs. Having median and mode numbers for the yards/carry relationship would be enormously helpful, but I don't imagine that we'll get those useful tenth of a yard figures until the NFL starts tracking the ball electronically. In the meantime it is useful to at least look at YPC and try to eliminate outliers. For instance, Willie Parker is a below average running back on most carries, but his total YPC is fairly impressive because of his long runs. Obviously if those long runs continue then there is no problem for the fantasy player, but as we've come to know through examples like Ashley Lelie, long plays are a much more unstable predictor than a large sample of shorter plays.

If we could somehow combine those mean/mode figures with information about down and distance, that would seem to be a much better indicator for which RBs would truly "break out" with more opportunities. Of course, you're still dealing with smaller samples and you're now expending an enormous amount of effort for information of questionable usefulness, so at some point it becomes a matter of the data being worth collection.

One more related note for Frank Gore fans:
2005 YPC with 72 yard run against Washington - 4.79
2005 YPC without it - 4.25

[...] is doing this on more carries, but his per-carry numbers are also universally lower. And besides, PFR has your excuses pre-doused with gasoline right here: You’ll hear this argument a lot: it’s easy to record a high YPC if you don’t [...]

Although this article is five years old, it cites Darren Sproles as an example of a talented young runner just waiting on an opportunity. Interestingly, he is still playing a supporting role and not getting many carries despite a 4.88 career rushing average (264 carries, 1288 yards). This might be his year, however, since he has doubled his rushing totals in each of the first 4 games of the season with 7 yards, 17 yards, 35 yards, 75 yards (18 total carries, 7.44 average).